Assessing the Impact of Soil on Manganese Contamination in Springs and Groundwater in the Shenandoah Valley, Virginia (thesis)

Abstract

A substantial fraction of the Shenandoah Valley, VA population relies on ground and spring water for domestic use. Manganese (Mn) is of particular concern in groundwater, as low-level chronic exposure to aqueous Mn concentrations >100 ppb in drinking water can result in developmental complications in children. Spring water and soil samples were collected throughout the Shenandoah Valley to supplement pre-existing groundwater well data from the National Water Information System and the Virginia Household Water Quality Program. Soil morphology, geochemical composition, and mineralogy were analyzed using scanning electron microscopy paired with electron dispersive X-ray spectroscopy, X-ray fluorescence, and Mn K-Edge X-ray adsorption near- edge structure spectroscopy. Factors such as soil type, soil geochemistry, and aquifer lithology were linked with each location to determine if correlations exist with aqueous Mn concentrations. While carbonate aquifers appear to have a protective effect by decreasing soluble Mn, those with more anoxic conditions such as shale and sandstone aquifers increase soluble Mn in both groundwater wells and springs. Analyzing the distribution of Mn in Shenandoah Valley drinking water sources, in addition to the geochemistry of associated soils, suggests that groundwater wells and springs within carbonate aquifers are preferable to those composed of black shale in regards to avoiding low-level chronic Mn exposure, and that soil weathering plays very little role in the redox chemistry of Mn. Furthermore, relationships between [Mn]aq in spring waters and Mn(II/III/IV) in soils indicate that oxic conditions yield greater proportions of harmless Mn(IV) oxides with less [Mn]aq and vice versa, but that, in certain transition zones, Mn(II) and Mn(IV) may react with each other to produce Mn(III), which may correspond with increased [Mn]aq.